Recently, a dye-sensitized solar cell have been paid attention to and it can be used as a power source of a various product without impact to its design and be manufactured with low cost. The dye-sensitized solar cell has a structure where a transparent substrate having a conductive layer (for instance, a layer of ITO (Indium Tin Oxide) film or FTO (Fluorine-doped Tin Oxide) film), a photoelectric conversion layer, a charge transport layer, and a counter substrate having a counter electrode conductive layer are build up. The technique where paste containing semiconductive particles such as titanium oxide is applied on the substrate and the paste is burned at a high temperature, is employed as a technique of forming a porous semiconductive layer which becomes the photoelectric conversion layer.
It is required that the dye-sensitized solar cell is manufactured with use of a resin substrate which is lightweight and low cost. Japanese Patent Application Laid-Open No. 2004-6235 (Document 1) proposes the technique where cathodic electrodeposition is performed on the substrate in electrodeposition liquid containing template agent to form a zinc oxide thin film containing the template agent, on the conductive layer of the substrate and then the template agent is desorbed to form a porous zinc oxide film. In the technique of the Document 1, the porous zinc oxide film can be formed on the resin substrate without the burning process which is inappropriate for the resin substrate.
However, there is a problem that productivity of the dye-sensitized solar cell in the technique of the Document 1 becomes low, because long process time is required for electrodeposition of the zinc oxide film and desorption of the template agent. So, in Japanese Patent Application Laid-Open No. 2008-62181 (Document 2), proposed is the technique where particle film of zinc oxide is formed on the conductive layer of the substrate by application of paste which contains zinc oxide particles and organic solvent, the particle film is immersed in immersion liquid which consists primarily of polar solvent to cause dissolution and redeposition of zinc oxide in the film, and therefore the zinc oxide film having high mechanical strength and high conductivity is formed. The productivity of the dye-sensitized solar cell with the resin substrate can be increased in the technique of the Document 2.
Japanese Patent Application Laid-Open No. 2005-259514 (Document 3) discloses the technique where a titanium oxide base layer is formed by application of paste of titanium oxide and this titanium oxide base layer is immersed in titanium oxysulfate solution to strengthen the bonds between titanium oxide particles and increase power generation efficiency of the dye-sensitized solar cell. In Japanese Patent Application Laid-Open No. 2000-8180 (Document 4), disclosed is the technique where catalytic process is performed on a non conductive base member with activating agent containing silver ion and thereafter it is immersed in zinc oxide deposition solution to form the zinc oxide film on the base member by the electroless method.
In the meantime, although the bonds between the zinc oxide particles are strengthened by immersing the particle film of zinc oxide into the immersion liquid in the technique of the Document 2, adhesion between the zinc oxide film and the conductive layer is not secured (actually, it is considered that the zinc oxide film adheres to the conductive layer by only mechanical engagement between a convexo-concave surface of the zinc oxide film and a convexo-concave surface of the conductive layer). As the result, there is a case where the zinc oxide film falls off from the substrate in the downstream processes of manufacturing of dye-sensitized solar cell.